## 题目描述：

The Employee table holds all employees. Every employee has an Id, a salary, and there is also a column for the department Id.

```+----+-------+--------+--------------+
| Id | Name  | Salary | DepartmentId |
+----+-------+--------+--------------+
| 1  | Joe   | 70000  | 1            |
| 2  | Henry | 80000  | 2            |
| 3  | Sam   | 60000  | 2 ...```

## 题目描述：

Suppose that a website contains two tables, the Customers table and the Orders table. Write a SQL query to find all customers who never order anything.

Table: Customers.

```+----+-------+
| Id | Name  |
+----+-------+
| 1  | Joe   |
| 2  | Henry |
| 3  | Sam   |
| 4  | Max   |
+----+-------+
```

Table ...

## 题目描述：

Given a binary tree, return the postorder traversal of its nodes' values.

```For example:
Given binary tree {1,#,2,3},
1
\
2
/
3
return [3,2,1].```

Note: Recursive solution is trivial, could you do it iteratively?

## 二叉树后序遍历的非递归实现 作者是 在线疯狂 发布于 2015年1月19日 在 数据结构.

二叉树的后序遍历很容易采用递归方式实现：

``````void postOrderTraversal(BinaryTree *p) {
if (!p) return;
postOrderTraversal(p->left);
postOrderTraversal(p->right);
cout << p->data;
}
``````

```树的删除。为了释放树结构的内存，某节点在被释放以前，其左右子树的节点首先应当被释放掉。

## 题目描述：

Given a binary tree, return the inorder traversal of its nodes' values.

```For example:
Given binary tree {1,#,2,3},
1
\
2
/
3
return [1,3,2].```

Note: Recursive solution is trivial, could you do it iteratively?